Method for flame-proofing combustible materials and product resulting therefrom



Dec. 20, 1932. E. OCKER 1,891,258

METHOD FOR FLAMEP G COMBUSTIBLE MATERIALS AND PROD THEREFROM C CR ROOFIN UGT RESULTING led Feb. '14, 1

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Patented Dec. 20, 1932 UNITED STATES PATENT OFFICE mnsr G. OBOG KERQOI' BELMONT, MASSACHUSETTS, ASSIGNOR TO ARTHUR D. LITTLE,

INCORPORATED, OF CAMBRIDGE, MASSACHUSETTS, A CORPORATION OF MASSACHU- ame mnon iron rmnn-raoorme comnus'rmm MATERIALS AND rnonuor ansun'rmo 'rnnrmraom I Application filed February 14, 1924. Serial No. 682,914.

This invention relates to substances, ineluding electrical insulators, so modified or treated as to inhibit the propagation of flame, and to a way of treating such substances ada ted to reach these results.

ith many commercial materials which are inherently combustible (but which are, on account of other valuable properties, preferable to non-combustible substances for their several uses) it is desirable and sometimes required by re ulatory statutes that the materials shall be ame proof. By flame proof is meant a quality causing ignition of the material to be more diflicult and the natural tendency of the material to support progressive combustion to be measurably d1- minished or more or less completely suppressed. Treatment to cause'the materials to have these qualities is known as flame proofm Tn such cases, it is not always desirable to so completely alter the characteristics of the material as to render it absolutely fireproof or non-combustible though in special instances this de ree of protection may be advantageously e ected.

Heretofore, the expedients resorted to for this purpose have generally consisted in 1mpregnating the material with a non-comb ustible salt or compound which, upon becoming heated, is intended either to dissociate into a non-combustible gas or flux over the surface, sealing the interior of the material from contact with the air. A common objection to such treatment is that the supposed functions of the compounds used are only partially effective in practice and secondly, that' such compounds are electrical conductors and not sufliciently inert chemically.

Combustion being a rapid oxidation of a substance which takes place at or above a given tem erature dependent upon the character of t e substance, progressive combustion or flame propagation requires that this temperature be maintained and transferred, and that a continued interaction between oxygen (as of air) andthe substance in question, shall take place.

The materials thus far used for flame proofing have not affected the first mentioned requisite for propagating combustion and have counteracted the second onl to a slight degree as by flowing over the eated in temperature as a result of combustion sufliciently to maintain, or to propagate in themselves, a temperature sufliciently elevated to continue their own combustion. When exposed to conditions of elevated temperature, such materials may be expected to inhibit flame, of themselves or their environing combustibles. If the oxide of the material chosen should form a vapor at a relatively low temperature, the result is further to inhibit flame by the formation of a zone of noncombustible vapor.

I have discovered that the element selenium, for example, although itself combustible, has the property of inhibiting, even when present in relatively minute quantity, the combustion of otherwise combustible material with which it is associated, as for example fabrics or structures of vegetable fibers;

Furthermore, the element imparts this property to certain at least of itscompounds, this being true of sodium selenite, selenious and selenic acids among others, so that materials so protected by the element or its compounds are thereby rendered flame proof.

The present invention accordingly comprises the treatment of a combustible material witha suitable compound or material of the class indicated for the purpose of rendering such material difiicult of ignition or flame proof. The treatment may beefl'ected in any suitable manner, but it is preferable to use the substance in finely divided condition and to impregnate or coat the surface therewith either in powder form or in the form of a liquid suspension, solution or paint.

A typical example of the application of the invention will be described in relation to flame proofing electrically insulated wire with a powdered substance adapted to produce the required effects, for which purpose the element selenium is peculiarly efl'ective. Such wire ordinarily has a covering of rubber and an outer covering of a textile such as paper or cotton, braided, wound or otherwise applied. The treatment may be carried out upon the wire either before or after the textile covering has been applied or it may be applied to the covering itself.

For the purpose of explaining the invention, the accompanying drawing in the nature of a diagram illustrates one flame-proofed article, an insulated wire, by way of specific exemplification of the genus of such articles within the invention. In this drawing, the figure is an elevation partly in section.

The particular manner of applying the flame proofing material may be varied according to the specific conditions to be encountered. In some instances it may be found practicable to merely cover the wire with the finely divided element alone, as by dust-ing or compressing a powder of the element into the surface of the material, and then making the textile cover around it.

A procedure which is generally preferable, consists in preparing a paste, for example, with a water solution of dextrine and powdered selenium, preferably the amorphous gray allotropic form (150-300 mesh), substantially in the following proportions by weight:

7 parts water 5 parts'dextrine 5 parts selenium The wire 1, already covered by the plastic or gummy flexible insulatin coat 2, such as one of the rubber compoun s, is then drawn through the mixture, a thin layer 3 of which will adhere to the surface. A textile cover 4 for example of cotton, paper ramie, or silk may then be braided or otherwise applied over the exterior surface, and the treating mixture will serve to retain the covering thereon as well as to hold the selenium powder in suspension. Upon drying, the selenium will remain in a uniformly distributed layer between the fabric covering 4 and the gummy insulation 2.

If a wire so treated is ignited the textile elements of the cover will burn in the area so ignited. However, the flame will not spread beyond this area, but presently the incandescent portion is found to be separated from the wire, leaving a zone of substantial extent (which is relatively cool) between the incandescent portion and the wire, which zone gradually widens, and the flame, thus removed from the wire, goes out.

Whatever the nature of the combustion tests on the described specific instance of the article of manufacture of this invention, there is visible evidence of the formation of red vapors presumably containing selenium oxide or selenium or both, and ossibly selenium nitride, these vapors constitutin a combustion-inhibiting zone of appreciable extent which rapidly develops after the initial ignition of the combustible elements of the wire.

Another feature of the invention is demonstrated by comparison of a treated wire according to this invention with the behavior of insulated wires otherwise treated. The latter when ignited and extinguished at one point are found to have lost their flame proof characteristic in lengths adjacent to the portion so tested. \Vhen treated in accordance with the present invention the testing of one portion in this manner does not diminish in any wise the effective protection of any other part of the wire.

It will now be clear that whatever the true explanation of the observed phenomena, the mode of treatment and the resulting article of this invention is useful wherever flameproofed combustihles may desirably be employed. Vhile a preferredmatezial and an a important use have been described, the invention is generally applicable to the flameproofing of combustible materials.

Compounds of selenium, in the practice of the invention, may be employed either in solution or in comminut-ed form with much the same effect. For example, selenium oxychloride, sodium selenite, selenious acid and selenic acid, although not quite so advantageous as the elemental substance, may be employed with beneficial effect. It will be observed that these substances are adapted to reduce to elemental selenium on the application of heat, whereupon the resultant behavior of the selenium accrues, with the effect of the elemental application.

I am not to be understood as excluding other elements than selenium or the alloys or simple compounds of elements, since it is obvious that any substance. capable of combinin directly with oxygen (of the air) but not 0% supporting its own combustion (and having as well the other properties made use of in the instance of selenium, suchas nonvolatility at ordinary temperature but appreciable volatility at the combustion temperature of the material flame roofed) will be effective if not disqualified or oher reasons. Arsenic is an-example of such an element. The extremely poisonous character of its compounds, however, precludes its use in many usual situations.

I claim:

1. An insulated wire having a portion including selenium for flame proofing.

2. An insulated wire flame proofed with a substance containing selenium carried coextensively with the extent of the wire.

3. A flame-proofed material having distributed thereon finely divided selenium.

4. A flame-proofed material having distributed thereon selenium in its gray allotropic form.

5. A fiame-proofed material having distributed thereon a substance containing elementary selenium at the temperature of combustion of the material.

6. A flame-proofed material having distributed thereon a finely divided substance containing selenium.

7. A combustible material fiame-proofed by a coating containing selenium.

8. A combustible material fiame-proofed by a coating containing selenium and another substance.

9. A combustible material flame-proofed by a coating containing selenium and oxygen.

10. Combustible material flame-proofed by the presence thereon of a suspension of finely comminuted gray selenlum in an organic substance.

11. An insulated Wire comprising a core of electrically conducting material, a coating of insulating material applied thereover, a second coating comprising selenium and a binding medium applied over said first-mentioned coating, and a textile covering applied over said second coating.

12. An insulated wirecomprising a core of electrically conducting material havin a coating of rubber insulating material applled thereon, and a second coating including selenium applied directly on said first-mentioned coating to render the insulated wire resistant to flame.

13. A flame-proof insulated wire having a coating comprising selenium and a binding medium applied on rubber insulation. Signed by me at Cambridge, Massachusetts, this 12th day of February, 1924.

ERNEST C. CROCKER. 

